Research On Technology And Method Of Detecting Boundary Layer Parameters Based On Various Lidars

The vertical structure of the atmospheric boundary layer has an important impact on the atmosphere-earth circle interaction.The earth circle here includes human activities,biosphere,hydrosphere,cryosphere and solid earth.The state of the atmospheric boundary layer is essential for the exchange process between the earth and the atmosphere,because the layering of the atmospheric boundary layer can regulate or change the vertical and horizontal transmission of energy,momentum,moisture,or trace substances.Therefore,the vertical structure of the boundary layer,the height of the atmospheric boundary layer and the height of the mixed layer determine many atmospheric processes,especially the tropospheric processes,which describe the turbulence and the mixing of pollutants(such as aerosol distribution,convective activities and cloud formation)are essential.Therefore,the detection research of vertical structure is one of the main tasks of the experimental boundary layer,so this paper mainly discusses the vertical structure of the atmospheric boundary layer,especially the height of the boundary layer and the height of the mixed layer.The height of the boundary layer can be obtained from sounding data,but the sounding data is usually only 2 to 4 data one day,so the time resolution is not enough.There is no way to invert the continuous change of the height of the boundary layer for one day.The height of the boundary layer can also be obtained by inversion of aerosol data.But Luo Tao pointed out that although aerosol-based methods perform well on the ocean,aerosol structures usually cannot provide a reliable boundary layer height on land.For the height of the mixed layer,it can be obtained with vertical wind field data,but the traditional fixed threshold variance method is higher when the turbulence is strong and lower when the turbulence is weak,and cannot solve the error problem of the height of the mixed layer when there is a vertical wave.Because there are not many stations that can provide all-day Raman lidar water vapor data and other related supporting detections(such as sounding data and vertical wind field data),so we choose the SGP(Southern Great Plains)site which locate in the south of north-central Oklahoma,the Doppler lidar and Raman lidar data from the SGP site are used as the main data source in this paper.The main content of this article is to use the data of the Southern Great Plains site to solve the above algorithm and do some statistical exploration:First,we use the improved Douglas-Peucker(DP)algorithm to obtain the boundary layer height based on the water vapor data of the Raman lidar.This paper uses Raman lidar water vapor data for the first time to retrieve the diurnal variations of the height of the boundary layer for many years;and optimization algorithm combining threshold algorithm,slope method and DP algorithm is proposed to retrieve the height of the boundary layer and compare the results with the sounding data.The results show that the height of the boundary layer based on Raman lidar is in good agreement with the sounding data.Secondly,the vertical wind field data of Doppler lidar is used to invert the height of the mixed layer by using a combination of variance and wavelet algorithm.This paper proposes a dynamic threshold method based on the traditional variance algorithm,but this method cannot solve the problem of the height of the mixed layer when there is a vertical wave.Furthermore,the dynamic threshold method is improved,which can effectively identify the existence of vertical waves,but the height of the mixed layer is not smooth enough.Then we propose a wavelet algorithm to calculate the height of the mixed layer.The results show that the wavelet method can obtain the accurate height of the mixed layer,but when the eddy size of tubulence is too large,the large-scale eddy current may also be filtered out,resulting in errors.On this basis,we use the different characteristics of the turbulent energy distribution of different eddy sizes under the wavelet algorithm to distinguish between large-scale turbulence and small-scale turbulence,and then use the wavelet algorithm for small-scale eddy and the improved dynamic threshold method for large-scale eddy.In this way,the height of the mixed layer can be accurately reversed.Because the distribution of eddy sieze is particularly important for meteorological model research,we used the fast Fourier method to study the distribution of eddy size.Then,based on the work of the above improved algorithms,this paper uses the long-term observation data of Raman Lidar and Doppler Lidar at the southern Great Plains station to study the diurnal variations of the boundary layer height and the mixed layer height under different weather conditions.The results show that the mixing layer of fine weather rises faster than the cloudy days;In fine weather,the height of the mixed layer will rise quickly and be consistent with the boundary layer,and then the mixed layer and the boundary layer will change together.The diurnal variation of the average boundary layer height and mixed layer height in the week under warm weather are calculated.The results show that the duration and start time of the mixed layer are consistent with the sunshine time.The diurnal variation of the boundary layer height in mid-summer is smaller than that in early summer and late summer.Finally,although lidar technology has been constantly developing,there are still many deficiencies,such as the Raman lidar echo signal is very weak,and the SNR(Signal-to-Noise Ratio)during the day is low.For this reason,this paper proposes the heterodyne amplified Raman lidar technical,which uses the water vapor Raman signal and nitrogen Raman signal of the local oscillation excited by the seed light locally and performs coherent detection with the atmospheric echo signal after frequency shifting through the acousto-optic modulator.In principle,this method can greatly improve the SNR of Ramn Lidar.In addition,a frequency comb lidar that can simultaneously measure multiple parameters of the atmosphere is introduced.The technique of measuring the transmittance curve of the FP etalon using the WGM(Whispering Gallery Mode)light source is proposed,and the technique of measuring the polarization characteristics of the FP etalon using the WGM light source is introduced.